1. Field of the Invention
This invention relates to apparatus for perforating sheet materials. More particularly, this invention pertains to an adjustable perforating roller suitable for perforating sheet material, such as thin bioriented polyvinyl chloride, which is commonly utilized as a packaging or wrapping material. The invention is particularly suitable for perforating shrink wrap packaging materials.
2. Description of the Related Art
In the use of heat shrinkable film, especially in the packaging field, it has been found necessary to provide holes or apertures in the packaging materials. These apertures serve various purposes, including the release of air from between the film and package so that the film can be shrunk tight over the package.
Prior attempts to produce perforations in thermoplastic film material have encountered substantial obstacles. One prior art apparatus uses a heated, pin-carrying, film perforating roll in conjunction with an annularly grooved anvil roll to perforate film material. It has been found that this apparatus tends to produce longitudinally extending ridges in the perforated film which are generally undesirable. This apparatus also tends to produce uneven or nonuniform film perforations.
The heating of the perforating roll of the above-described apparatus inherently induces longitudinal roll expansion, particularly where long rolls are employed to handle large widths of film. Considerable difficulty has been encountered with respect to misalignment of the perforating roll pins in the anvil roll and annular grooves caused by such longitudinal expansion of the pin roll.
Perforating apparatus for placing small apertures in shrink wrap packaging materials to allow air to escape as the material is being shrunk around the package are conventionally comprised of a sleeve having multiple perforating pins, which can be fit over an idler roll. Because different sizes, shapes and locations of perforations are required, depending on the application, users often must have a number of different sleeves available for use in different applications.
This can be very costly, since special sleeves must be made or purchased for each separate application. Furthermore, because the diameter of the idler rolls often vary from machine to machine, multiple sleeves or sleeve spacers may be required in order to make identical perforations in the same material using different machines. Additionally, these sleeves are difficult to install and remove when different perforation sizes, shapes and/or locations are required. Also, is difficult to adjust the perforation pin sizes, shapes or locations without substituting one sleeve with another.
Thus, it is an object of the present invention to provide a perforating apparatus which does not require special sleeves for each separate application. It is also an object of the invention to provide a perforating apparatus which does not require heated perforating pins. It is a further object of the invention to provide a perforating apparatus which has a constant outside diameter and can be used on a number of machines for the same application without the need for spacers or other adjustment devices. It is still another object of the present invention to provide a perforating apparatus which is easily adaptable to a variety of applications which require different perforation sizes, shapes and/or locations. It is yet another object of the present invention to provide a perforating apparatus which is easily adaptable to a variety of applications without the need to install and remove a roller and/or sleeve. It is also an object of the present invention to provide a perforating apparatus which simplifies changing the perforation sizes, shapes and/or locations when required. It is a still further object of the present invention to provide a perforating apparatus which allows the perforation pin sizes, shapes or locations to be adjusted in a flexible manner and without requiring roller and/or sleeve removal.
Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art upon examination of the following, as well as by practice of the invention. While the invention is described below with reference to preferred embodiments for an apparatus for perforating packaging film to obtain proper shrinkage, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications, modifications and embodiments in other fields (including, but not limited to the perforating of photo, audio, and video film), which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.